The present invention provides polymer blends comprising the components    (a) from 40% to 95% by weight of at least one polyaryl ether copolymer constructed of            (a1) from 50% to 99.9% by weight of building units of the general formula I        
                having the following meanings:        t, q: independently 0, 1, 2 or 3,        Q, T, Y: each independently a chemical bond or group selected from —O—, —S—, —SO2—, S═O, C═O, —N═N—, —RaC═CRb, —CRcRd—, where Ra and Rb are each independently a hydrogen atom or a C1-C12-alkyl group and Rc and Rd are each independently a hydrogen atom or a C1-C12-alkyl, C1-C12-alkoxy or C6-C18-aryl group, at least one of Q, T and Y being other than —O— and at least one of Q, T and Y being —SO2—, and        Ar, Ar1: independently C6-C18-arylene, and        from 0% to 40% by weight of further building units II selected from segments of one or more thermoplastic polymers, and        (a2) from 0.1% to 10% by weight of at least one crosslinker V having at least three hydroxyl functionalities,                    the at least one crosslinker V being present in component (a) in converted form and the sum total of % by weight for (a1) and (a2) being 100% by weight,and                            (b) from 5% to 60% by weight of at least one hydrophilic polymer selected from polyvinylpyrrolidone, polyvinylpyrrolidone copolymers, polyethylene glycol, polypropylene glycol, copolymers of ethylene glycol and propylene glycol, water-soluble cellulose derivatives, polyamide, polyvinyl acetate and polyvinyl alcohol,where the sum total of % by weight for components (a) and (b) is 100% by weight.
The present invention also provides combinations of distinct components (a) and (b) for conjoint use. The invention further provides polymer membranes comprising the aforementioned polymer blends and also a process for their production and the use of the polymer membranes for producing dialysis filters. The present invention also provides dialysis filters comprising the aforementioned hollow fiber membranes.
Polyaryl ethers belong to the group of high performance thermoplastics and find utility in very demanding applications owing to their high thermal and chemical resistance, see G. Blinne, M. Knoll, D. Müller, K. Schlichting, Kunststoffe 75, 219 (1985), E. M. Koch, H.-M. Walter, Kunststoffe 80, 1146 (1990) and D. Döring, Kunststoffe 80, 1149 (1990).
Branched polyaryl ethers were developed to extend the given performance spectrum of polyaryl ethers. German Offenlegungsschrift DE-A 2305413 discloses branched polyaryl ether sulfones having, compared with linear polyaryl ether sulfones, a lower susceptibility to stress corrosion cracking, improved resistance to unsaturated polyester resins and also reduced flammability.
In Macromolecular Symposia 2003, 199, 243-252 a paper about the synthesis and characterization of branched polyaryl ethers discloses that the use of branched polyether sulfones generally improves the flowabilities of polyether sulfones, but worsens mechanical properties, such as toughness for example.
Owing to their low hydrophilicity and hence good resistance to hydrolysis, linear polyaryl ethers have for many years been used as membrane materials. For instance, S. Savariar et al., Desalination 144 (2002) 15 to 20 describe the use of polysulfone for producing dialysis membranes. Since polysulfone absorbs relatively little water, such dialysis membranes are typically produced using a hydrophilic polymer, for example polyvinylpyrrolidone (PVP), as an additive.
DE-A 10 2005 001 599 describes functionalized, branched polyaryl ether copolymers comprising sulfonated and nonsulfonated units. The sulfonated polyaryl ether copolymers are produced by sulfonation of the corresponding branched polyaryl ether copolymers. The reference mentions the use of the sulfonated copolymers for producing membranes. It also mentions polymer blends of the aforementioned sulfonated polyaryl ether copolymers and numerous blending partners, including polyvinylpyrrolidone. However, DE-A 10 2005 001 599 neither discloses blends of nonsulfonated branched polyaryl ethers nor discusses the particular requirements for use in the production of hollow fiber membranes.
The production of hollow fiber membranes for dialysis modules imposes particular requirements on any polymeric material. These are in particular the separation performance and the molecular weight cutoff and therefore the ability to filter out certain toxins in dialysis, and also a high durability under the conditions of sterilization and prolonged permanence of membrane properties.
For instance, EP 0509663 B2 describes dialysis modules having selectively permeable hollow fiber membranes based on a blend of polyether sulfone and a hydrophilic polymer such as for example polyvinylpyrrolidone or polyethylene glycol. EP 0615778 A1 discloses a process for production of hydrophilic membranes by using hydrophobic polymers such as polyether sulfones and of hydrophilic polymers by using polyvinylpyrrolidone.
However, mechanical properties in sustained use, proccessability in relation to production, and separation performance, in particular the molecular weight cutoff, are not always satisfactory for the materials used in existing dialysis membranes.